1. Field of the Invention
The present invention relates to a dual port Ethernet communication device with bypass function and, more particularly, to a dual port Ethernet communication device with bypass function which allows the dual port Ethernet communication device to bypass data received via one communication port to other communication port so that a terminal unit equipped with the Ethernet communication device can transfer the communication data to other terminal units even though a terminal port equipped with a relevant Ethernet communication device does not operate normally.
2. Description of Related Art
An Ethernet communication device is provided on various terminal units to allow a relevant terminal unit to perform Ethernet communication with other terminals. The Ethernet communication device is required to have only one communication port, when connected to a single communication network such as a personal computer (PC) using internet service.
Meanwhile, the Ethernet communication device is required to have a dual port, when terminal units are required to be connected in a closed loop manner.
As one specific example related thereto, a constant closed-loop system in a distribution system is proposed.
The constant closed-loop system is such that a closed loop is formed by a communication line together with a distribution line where each point is formed with a terminal unit for managing a circuit breaker at a corresponding position. Each terminal unit is connected to it own forward/backward terminal units via a dual port, so that all terminal units form a closed-loop to communicate with each other.
FIG. 1 shows a structure of the closed loop system formed by the terminal units, in which the terminal unit #1 11 to the terminal unit #4 14 have the dual communication port respectively and each terminal unit is connected to its forward/backward terminal units via the dual communication port.
In other words, the terminal unit #1 11 is connected to the terminal unit #2 12 and the terminal unit #4 14 via the dual communication port; the terminal unit #2 12 is connected to the terminal unit #1 11 and the terminal unit #3 13 via the dual communication port; the terminal unit #3 13 is connected to the terminal unit #2 12 and the terminal unit #4 14 via the dual communication port; and the terminal unit #4 14 is connected to the terminal unit #1 11 and the terminal unit #3 13 via the dual communication port.
Referring to FIG. 2, each terminal unit 12 has a port A 12-4 and a port B 12-5 as the dual port and two communication controllers 12-2 and 12-3 for performing the communication correspondingly to the ports respectively, in which each of the communication controllers 12-2 and 12-3 sends and receives the communication data to and from the data bus 12-1 of the terminal unit.
The communication controller A 12-2 transfers the communication data transferred from the data bus 12-1 via the port A 12-4 and transfers the communication data received from the port A 12-4 to the data bus 12-1.
Further, the communication controller B 12-3 transmits the communication data transferred from the data bus 12-1 via the port B 12-5 and transfers the communication data received from the port B 12-5 to the data bus 12-1.
At this time, if the terminal unit 12 fails to operate normally, it is difficult to implement an interface between each communication controller 12-2 and 12-3 via the data bus 12-1, and therefore the communication in the terminal unit 12 is stopped.
More specifically, the communication data cannot be received from the terminal #1 11 and then transferred to the terminal #3 13.
As such, when each terminal unit is connected with each other via the dual port, the communication may be stopped if any terminal unit fails to operate normally due to causes such as a break down.